The present invention relates generally to fuel systems, and, more particularly, to an apparatus and method for priming fuel systems of marine engines.
Many fuel systems, such as those found on electronically fuel-injected motors for use with marine vehicles, include a low-pressure fuel circuit and a high-pressure fuel circuit. The low-pressure fuel circuit typically includes an engine driven suction or lift pump that pulls fuel through a low-pressure fuel line connecting the vehicle fuel tank to an engine-mounted vapor separator. The vapor separator includes a float-activated needle and seat to control fuel depth within the vapor separator, and an electric fuel pump to increase the fuel pressure to the operating pressure of the high-pressure system, i.e., the electronic fuel injection system.
One of the purposes of such a dual-pressure system is to minimize the amount or length of on-board fuel line containing fuel at high pressure. A leak in the low-pressure line pulls air into the fuel line. In contrast, a leak in the high-pressure fuel line forces or leaks fuel out of the fuel line. Thus, by limiting the amount or length of high-pressure fuel line, the potential for undesirable accumulation of leaked fuel is reduced. Therefore, attempts are made to limit the length and position of the high-pressure fuel line. On outboard engines, the high-pressure fuel lines are typically restricted to the engine itself. Thus, any leaks from the high-pressure fuel line are likely to be contained under the cover or cowl of the engine. The leaked fuel will eventually drain into the body of water, a condition that, although perhaps undesirable, is far less dangerous than the leaked fuel accumulating in the marine vehicle itself. Similarly, on marine vehicles with inboard engines the use of high-pressure fuel lines is restricted to the engine compartment thereby limiting the accumulation of leaked fuel to the engine compartment.
A drawback to such dual-pressure systems is that heat rejection from the high-pressure fuel pump and the engine itself can cause the boiling and/or vaporization of the liquid fuel in the vapor separator, low-pressure lift pump and low-pressure fuel lines. This impedes fuel delivery to the high-pressure fuel pump, and can thereby cause rough engine operation and/or stalling. Therefore, dual-pressure systems generally require an additional cooling system that cools the vapor separator and/or high-pressure return fuel line, typically with cooling water drawn from the body of water.
The additional cooling system must draw power from either the engine or battery in order to operate, and is thus typically operated only during engine operation. Such a cooling system does not prevent the fuel from vaporizing during a hot soak condition, i.e., the time following engine shut-off and before the engine and high-pressure fuel pump have cooled down. During a hot soak, at least some of the heat dissipating from the engine and high-pressure fuel pump is absorbed by the low-pressure fuel remaining in the vapor separator, low-pressure lift pump and low-pressure fuel lines. This absorbed heat can cause vaporization of the low-pressure fuel. The vaporized fuel, in turn, pushes any liquid fuel remaining in the vapor separator and low-pressure fuel lines back into the fuel tank.
Restarting the engine from a hot soak condition, i.e., a hot restart, can result in stalling or rough engine operation if the liquid fuel remaining in the high-pressure fuel line is consumed before the low-pressure lift pump is able to refill the low-pressure fuel line and the vapor separator with liquid fuel. Some fuel systems incorporate a check valve between the lift pump and the fuel tank to reduce the amount of fuel that is pushed back to the fuel tank. However, vaporization of the fuel remaining in the low-pressure fuel line may still occur, and fuel between the check valve and fuel tank may run back to the fuel tank. In order to avoid stalling and/or rough engine operation upon hot restart, the lift pump must replace the volume lost due to the hot soak condition before the liquid fuel remaining in the high-pressure fuel line and vapor separator is consumed.
Therefore, what is needed in the art is an apparatus that reduces the need for a cooling system for the vapor separator and/or high-pressure return fuel line.
Furthermore, what is needed in the art is an apparatus that reduces stalling and/or rough engine operation on hot restart.
The present invention provides a fuel system for fluidly connecting a fuel tank with an engine.
The invention comprises, in one form thereof, a low-pressure fuel circuit fluidly connected to the fuel tank. A high-pressure fuel circuit is supplied with fuel by the low-pressure fuel circuit, and is fluidly connected to the engine. A priming fuel circuit includes a priming fuel conduit and a priming valve. The priming fuel conduit has a first segment and a second segment. The priming valve has an inlet and an outlet. The first segment of the priming fuel circuit fluidly interconnects the low-pressure fuel circuit and the outlet of the priming valve. The second segment of the priming fuel circuit fluidly interconnects the high-pressure fuel circuit and the inlet of the priming valve. The priming valve is operable to control a flow of fluid through the priming fuel conduit to thereby selectively fluidly connect and disconnect the high-pressure fuel circuit and the low-pressure fuel circuit.
An advantage of the present invention is that the cooling system for the vapor separator and/or high-pressure return fuel line can be of a reduced capacity or be completely eliminated.
Another advantage of the present invention is that stalling and/or rough engine operation during hot restart is reduced.